1. Field of the Invention
The invention relates to a plug connection for jaw stump models for the releasable securing of tooth crown segments or jaw segments to a model base, with a plug pin and a sleeve.
2. Description of the Related Art
In the context of dental treatment, if it is necessary to replace one or more teeth, or possibly even the replacement of a jaw segment, then the implants provided need to be specially manufactured and adapted for the patient in each instance. For this purpose, a dental impression of the patient is often produced, which then serves as an initial mold for a jaw stump model. This jaw stump model is an identical reproduction of the patient""s set of teeth. The region which is to be replaced in the patient""s oral cavity by the implant, for example a tooth crown segment, is removed from the model. A prefabricated implant blank can then be adapted step by step to the model, until it obtains the shape required for the patient""s treatment. The implant, which is specially prepared in this manner for the patient, can then be operatively secured in the oral cavity of the patient, without the need for complex preparation of the implant or secondary working.
For the adaptation of the implant to the jaw stump model, which precedes the surgical intervention, it is first necessary to secure the implant to the model. However, it is almost always necessary, during the course of the step by step adaptation and secondary improvement, for the implant to be removed from the model several times, and then secured to the model again. In this respect, it is necessary to ensure that the implant is secured to the jaw stump model again in exactly the same position following each interim removal. Otherwise, it would not be possible to precisely adapt the implant to the model and therefore to the patient.
For this reason, it is known to secure plug pins in the implant, by means of which the implant can be fitted into corresponding bores in the model. However, given that the model may be made of plaster, for example, there is a risk of the bores becoming damaged during each securing or removal of the implant as a result of material wear, so that precise positioning of the implant is not guaranteed on a long-term basis.
Plug connections are described, for example, in Laid-Open Specification EP 0 335 285 A2, which, in addition to a plug pin, also comprise a sleeve which is embedded in the jaw stump model. The sleeve is made of sufficiently resistant material, such as metal, and prevents possible damage to the jaw stump model by the plug pin.
Because a rotationally symmetrical plug connection of this type cannot prevent rotary movements of the implant about the pin axis, additional measures are required for reliable and reproducible securing of the implant to the jaw stump model. Thus, it is known to prevent a rotary movement of the implant by means of two plug connections fitted adjacent one another (DT 26 25 950 A1). However, this is associated with a high labor outlay, and requires a large amount of space, which is not always possible or tenable.
If the sleeve and the plug pin are not aligned exactly axially parallel in plug connections of this type, then the plug pin often tilts in the sleeve during securing and removal of the implant from the model. The resulting stresses can damage both the jaw stump model and, in particular, the securing of the plug pin in the implant, which can result in a loss of precision in the manufacture of the implant. The more plug connections used for an implant, in order, for example, to rule out rotary movements of the implant, the higher the requirements for exact alignment of the plug connections in order to prevent stresses or tilting.
In a known plug connection (DE 43 00 926 A1), the plug pin has a slightly conical design, so that sufficiently secure positive and frictional locking between the plug pin and the sleeve is only produced once the plug pin has fully penetrated the similarly conically tapering sleeve. By means of knob-like raised elements on the inside of the sleeve, made of plastics material, the retaining force of the plug pin in the sleeve can be increased. However, here, too, a secure connection of the plug pin in the sleeve is only guaranteed in the case of an exact axially parallel alignment of the two parts. In addition, in order to prevent a rotary movement of the implant, it is necessary to secure the latter to the model by means of at least two plug connections of the above type.
Ever advancing developments in dental medicine, in the use of implants, demand increasing precision in the manufacture and adaptation of the implants. As a result of the constant and high loading of a fitted implant in the oral cavity, for example during chewing, a best-possible adaptation of the implant to the respective patient is a prerequisite for a secure connection of the implant to the jaw of the patient which can withstand these stresses on a long-term basis.
It is therefore an object of the invention to design a plug connection for jaw stump models, of the generic type, so that a reliable and easily releasable securing of the implant to the model base is possible, rotary movement of the implant about the axis of the plug connection being eliminated. Furthermore, stresses and tilting of the plug pin in the sleeve are eliminated, even in cases where the two parts are not aligned exactly axially parallel.
This and other objects are achieved according to the invention, in which the plug pin is connected in a snap-locking fashion with the sleeve, and in which rotational locking prevents rotary movement of the plug pin in the sleeve.
The present invention thus relates to a plug pin, connected in a snap-lock fashion with the sleeve, whereby rotational locking prevents a rotary movement of the plug pin in the sleeve. A snap-lock connection of the plug pin and the sleeve results in a sufficiently stable securing of the implant to the model base. Consequently, the plug pin can be constructed in such a manner that it can be introduced almost fully into the sleeve with a clearance significantly facilitating handling. Only in the end position prescribed by the snap-lock connection is the plug pin fixed in a predetermined position. In order to remove the implant, it is only necessary to release the snap-lock connection between the plug pin and the sleeve. The plug pin can then be fully withdrawn from the sleeve, without thereby generating stresses or without the danger of the plug pin tilting with the sleeve. As a result of this snap-lock connection, a uniform penetration depth of the plug pin in the sleeve is automatically ensured. Only once the implant is arranged in the provided position on the model base is the snap-locking connection between the plug pin and sleeve produced.
As a result of the rotational locking, a rotary movement of the plug pin in the sleeve is ruled out. Consequently, it is possible, using a single plug connection, to prevent rotary movement of the implant secured to the model base. Additional plug connections are therefore unnecessary. In addition to resulting in a saving in labor and materials, this also means that a plug connection of this type can also be used in the case of very small implants having a small contact surface area with the model base.
The maximum penetration depth of the plug pin in the sleeve is defined by an abutment. An abutment of this type can be provided using simple means in manufacturing technology, for example by the length of the plug pin or a projection projecting radially from the plug pin. In this manner, in addition to the snap-locking connection, the maximum penetration depth of the plug pin in the sleeve can be reliably and precisely determined using little outlay.
According to an advantageous embodiment of the inventive idea, the plug pin comprises, at its end facing the sleeve, a spring element with recesses for a snap-locking connection with the sleeve. When the plug pin is introduced into the sleeve, the spring element is slightly bent by a projection projecting into the inner chamber of the sleeve, until the spring element is connected in a snap-locking manner with the projection of the sleeve in the region of the recess provided. The force necessary for the deformation of the spring element can be determined by the design and material of the spring element. In this respect, the spring element is expediently constructed in such a manner that, on the one hand, a sufficiently secure snap-locking connection of the plug pin and the sleeve is ensured, whilst on the other hand, damage to the sleeve or plug pin, or the implant associated therewith as a result of excessive stresses, is ruled out.
Advantageously, the spring element comprises a substantially cylindrical basic element, which is divided into a plurality of spring tongues by at least one continuous longitudinal slot extending as far as the end facing the sleeve. In this manner, it is possible using simple means to produce a robust spring element which is substantially independent of the alignment of the plug pin in the sleeve. Additional components fitted to the plug pin are unnecessary for a spring element of this type. By appropriately dimensioning the longitudinal slot, the force required for a deformation of the spring tongues can be prescribed as a function of the material of the plug pin.
According to one embodiment of the invention, the projection which projects into the inner chamber of the sleeve is constructed as an annular circumferential bead. In association with a corresponding recess on the spring element, it is thus possible to effect a snap-locking connection between the plug pin and the sleeve along the entire circumference. The retaining force necessary for securedly fixing the plug pin in the sleeve can be uniformly distributed over the annular circumferential bead and need not be applied locally. The snap-lock connection can thus be effected in such a manner that it is distributed over a plurality of spring tongues, so that a low bead height, and therefore a slight bending of the spring tongues during the introduction of the plug pin, is sufficient for a secure fixing of the implant to the model base.
The recess of the spring element can also be constructed as a continuous cross bore, which extends perpendicular to the pin axis and engages around a projection constructed as a locking pin projecting into the inner chamber of the sleeve. The function of the annular circumferential bead constricting the sleeve cross section can also be fulfilled by a locking pin arranged transversely in the inner chamber of the sleeve. When the plug pin is introduced into the sleeve, the individual locking tongues are not compressed, but are instead bent slightly outwards. The recess in the spring element provided for the snap-locking connection can be realized in a simple manner, in terms of manufacturing technology, as a cross bore extending through the spring element. In the end position of the plug pin, the locking pin is disposed in the region of the cross bore of the spring element, which then engages around the locking pin in a snap-locking manner. Since both the cross bore in the spring element of the plug pin, and the locking pin in the inner chamber of the sleeve, are aligned along a common axis perpendicular to the pin axis for a snap-locking connection, a specific azimuthal position of the plug pin is thereby also prescribed. Any slight twisting away from this position results in a spring force counteracting this rotary movement.
Advantageously, in the end position of the plug pin in the sleeve prescribed by the abutment, the recess of the spring element has a defined degree of offset relative to the projection which projects into the inner chamber of the sleeve, so that the plug pin is additionally fixed in the end position with a permanently acting tensile force. The spring action of the spring element generates a force which pulls the plug pin into the sleeve interior. Without the abutment defining the end position, the plug pin, as a result of this tensile force, would penetrate the sleeve to such a degree that the recess of the spring element would come to rest above the projection which projects into the inner chamber of the sleeve, and the deformation of the spring element would be minimized. It is at least necessary to overcome this permanently acting tensile force, in order to remove the plug pin from the sleeve. In this manner, accidental slight slipping of the plug pin out of the sleeve is prevented. This type of design, with the snap-lock connection between the plug pin and the sleeve, results in a precisely defined and reproducible securing position of the implant on the model base. This is true even in the case of deviations in the dimensions of the plug pin and the sleeve, which are unavoidable using current manufacturing technology, and in the case of an alignment of the two components which is not exactly axially parallel.
According to an advantageous embodiment, the plug pin comprises a substantially cylindrical basic form, with a non-rotationally symmetric rotational locking section which projects radially, at least in part, and engages in the region of the sleeve opening with a matching inner chamber of the sleeve. Only when the plug pin is almost fully introduced into the sleeve do laterally projecting, non-rotationally symmetric projections of the plug pin engage with the sleeve. In the region of the sleeve opening, the sleeve is designed in such a manner that the rotational locking section of the plug pin can only be introduced into the sleeve in a given alignment. Once the rotational locking section has been at least partially pushed into the sleeve, a rotation of the plug pin is no longer possible. In this respect, the length of the rotational locking section can be adapted to respective requirements.
According to another embodiment, the rotational locking section comprises a radially projecting, substantially cylindrical basic form, with at least one flattened section extending parallel to the plug pin axis, and in the region of the sleeve opening, the sleeve comprises a matching, inwardly projecting projection. A flattened section of this type, in the otherwise cylindrical rotational locking section, can be produced during manufacture with little outlay. A matching design of the sleeve opening only allows for a single alignment of the plug pin in the sleeve. A counter pressure of the sleeve acting upon the flattened section counteracts a rotation of the plug pin in the sleeve.
According to a further advantageous embodiment, the diameter of the spring element is, at most, only as large as the smallest internal diameter of the sleeve in the region of the sleeve opening. In this embodiment, the spring element of the plug pin can be introduced into the sleeve unimpeded and independently of the alignment of the plug pin. Already, at this stage, the implant can no longer accidentally fall from the model base. An exact alignment of the implant is considerably facilitated when the plug pin is partially introduced.